1. Field of the Invention
The present invention relates generally to the treatment of high pressure, high temperature slurries and more particularly, but not by way of limitation, to a process for efficiently reducing the pressure on such slurries.
2. Description of the Prior Art
In certain chemical processes it often times is necessary to reduce the pressure of high temperature, high pressure slurries to substantially lower pressure conditions. Such pressure reduction usually is achieved by passing the slurry through throttling or reducing valves.
Such valves are subjected to extensive wear and erosion because of the high pressure drop and because of the high temperature exposure of the valve seats. The presence of suspended solids in the slurries accelerates the erosion as the particles are subjected to a high velocity head by the pressure drop. Finally, the flashing that accompanies the pressure reduction across the valve also is a factor in eroding the valves. Even with the use of hard erosion-resistant materials for the construction of the seats and plungers of pressure reducing valves, the valves used for pressure reduction of high pressure, high temperature slurries require frequent replacement. In a commercial processing plant, there may be a large number of pressurized vessels that are utilized for slurry service and which have slurry effluents that are subjected to large pressure reduction. It is understandable therefore that frequent replacement of the large number of pressure reducing valves in such commercial processing plants is undesirable for the obvious reason that this results in excessive operating and maintenance expense.
There are other problems encountered in the use of throttling valves to effect pressure reduction of high pressure, high temperature slurries. Thus, slurries having high concentration of solids contained in low boiling liquids, the flashing taking place across the throttling valves promotes the buildup of solid material within the valves, and this condition often leads to extreme fouling and plugging of the valves. Additionally, the depressurized solid material produced by the spontaneous vaporization of the liquid component of the slurry often results in the formation of one solid mass, making the resultant mass difficult to handle in subsequent processing steps.
The present invention provides an improved technique for removing high pressure, high temperature slurry solutions from processing vessels whereby a minimum number of pressure reducing valves are required, as a single reducing valve can service a plurality of such processing vessels, thereby reducing the frequency of valve replacement. Furthermore, the amount of flashing that occurs across the reducing valve is minimized by the present invention, and the depressurized product is consequently maintained as a readily flowable slurry.